This reminds me a bit of a classic paper called "1/N". It compared a portfolio of putting equal money into each security, vs a bunch of fancier approaches. The 1/N almost always won.
I fear I'm misunderstanding you. Are you saying despite having higher returns, the higher risk makes this strategy worse? That really feels like handwaving to me, since the only thing I care about is ROI. I understand nonlinearity and how it could tank your investment, but if it doesn't and you make more money then you're criticizing something that never happened. The higher risk is already baked into the ROI, because it includes the times that failed. The point is, in aggregate, you make more money - and most of the time that is the only thing I care about when investing.
Or am I misunderstanding you?
> it could tank your investment, but if it doesn't and you make more money then you're criticizing something that never happened
This way of reasoning is basically survivorship bias in a nutshell, and per my direct experience as a financial professional has brought down many investors who were too confident about their "strategy".
To bring this argument to the extreme: if you cared only about ROI, you could just go long some penny stock with exaggerate leverage and make big money "unless proven otherwise". In practice, what happens is you get euphoric for a couple days while you see the money shoot up to the sky, and then lose all of it to a margin call at the opening the very next day. I've seen it happen with my own eyes.
As a highly simplified, unrealistic example - let's say strategy A has an average return of 5%/year with max drawdown of 20%, and strategy B has an average return of 10%/year with a max drawdown of 50% (here max drawdown being a highly simplified proxy for risk). Theoretically, you could use leverage to go 2.5X long strategy A to achieve a return of 12.5%/year with a max drawdown of 50% (minus cost of the leverage - depending on how you do this, cost could be fairly small). This might do better, risk-adjusted, than just doing strategy B by itself.
There’s lots of metrics that try to balance the risk and reward. Often, the risk is based on the volatility of the asset. The common alpha metric does this by incorporating the assets volatility compared to the overall market volatility. There’s others like Sharpe ratio etc.
Factoring that volatility is particularly important in long-term investing so your choices don’t, as you say, tank your investment. So maybe you interested in cyclicals over the last nine months and your investments went gangbusters. Does that mean that same strategy will work in perpetuity? Probably not, because cyclicals tend to have high volatility. Risk -adjusted metrics attempt to quantify that risk.
And obviously there’s mathematical measurements where one tries to get the highest return per unit of risk. It’s possible that these returns might be higher but fall under the curve.
They compared equal weighting, but did they also check market-cap weighting?